Assuming that a vehicle is a rigid body and is situated on a plane movement, the vehicle can be explained by a translation motion and rotational motion. Forces relative to each of the motions are mainly frictional forces acted between a road surface and tires. There have been proposed various types of vehicle motion controls to generate a difference of braking and driving forces among four wheels (right-and-left-wheel differential torque) of four wheels and to control directly a yaw moment, in addition to the vehicle motion control using a lateral force of the tires to be used for vehicle etc., the front-and-rear-wheel steering vehicle.
As is feasible to the above mentioned proposal, there is a right-and-left-wheel differential torque generator having the following functions such that:
1. A brake force is distributed,
2. An engine driving torque is distributed to the right and left, and
3. A rotating electric machine is used.
The items 1 and 2 are close to part of the same advantages of the present invention. However, the item 1 is used for a mechanical brake apparatus to act on a vehicle in a decelerating direction alone. The item 2 is used for distributing the engine driving torque, and is affected considerably by an acceleration operation by a driver. For this reason, the foregoing technique is different in that the invention uses the rotating electric machine to attempt to generate the right-and-left-wheel differential torque at an arbitrary timing, so that it is clearly departed from the invention. Therefore, the technique with use of the rotating electric machine as indicated in the item 3 will be described as a background art.
There have been disclosed the rotating electric machine of the item 3 used in JP-A-11-30293, JP-A-11-91383 and JP-A-2004-322793.
The JP-A-11-30293 discloses a yaw moment controller of a vehicle characterized by: a pair of electric motors incorporated into left and right wheels to be able to drive independently for each of the left and right wheels; a battery connected to the electric motors; driving condition detecting means that detects a driving condition of the vehicle; moment calculation means that calculates a target yaw moment of the vehicle in response to the detected driving condition; torque calculation means that calculates respectively left-right-wheel torques to obtain the target yaw moment in accordance with the calculated target yaw moment; and a motor control circuit connected between the battery and the pair of electric motors to control respectively the pair of electric motors in response to the respective calculated torques. An object of the invention is to provide a yaw moment controller of the vehicle to control the yaw moment of the vehicle in high accuracy.
Further, JP-A-11-91383 has proposed a turning assist apparatus of a vehicle in which differential rotation generating means is provided to generate a differential rotation between the left and right driven wheels so that an outer-wheel-side driven wheel is increased in speed faster than an inner-wheel-side driven wheel on turn, characterized in that the differential rotation generating means is constituted so that it has a driving source to add a torque to the outer-wheel-side driven wheel to increase a speed faster than the inner-wheel-side driven wheel, the driving source is constituted by an electric motor, and a stator and rotor of the electric motor are coupled respectively to one driven wheel and the other driven wheel. An object of the invention is to provide the turning assist apparatus so that a brake force is not applied to the driven wheels as a whole.
Further, JP-A-2004-322793 has proposed a left and right wheel driving apparatus of a vehicle for providing a turning assist of the vehicle by generating a reverse direction torque at a right-side wheel and left-side wheel as an identical magnitude by at least a single electric motor, in which the left and right wheel driving apparatus is characterized by: decelerating command detection means that detects a decelerating command of the vehicle; electric motor adjustment means that makes a torque of the electric motor low when a decelerating command—2Tx is detected as a brake torque in terms of torque at the wheels under condition where the turning assist is being functioned; and brake means that adjusts a frictional brake torque of the left and right wheels so that a difference of a left and right wheel torque becomes 2Ty and the brake torque becomes—2Tx in response to a torque adjustment of the electric motor. An object of the invention is to provide the left and right wheel driving apparatus of the vehicle capable to carrying out the turning assist sufficiently by a small size electric motor when a brake operation is carried out under the turning assist condition. Therefore, a cooperative movement of the electric motor and frictional brake is carried out so that a loss of the electric motor can be reduced, consequently, a fuel consumption of the vehicle can be made good.